HEAVENLY BODIES 



463 



more readily through our atmosphere, while the blue rays are 

 refracted. 



Heat of the Sun. It has been estimated that if the heat of the 

 sun were produced through the burning of coal it would require 

 about 8 trillion tons per second enough coal to supply the entire 

 world for many years. How 

 the sun produces heat has 

 been discussed on page 137. 



Size of the Sun. The 

 volume of the sun is one 

 million three hundred thou- 

 sand times that of the earth 

 and its weight about 198, 

 000,000,000,000,000,000,00?,- 

 000,000 pounds. So great is 

 this weight that a man 

 weighing 150 pounds on 

 earth would weigh about 2 

 tons on the sun. Even his 

 feet would weigh several 

 hundred pounds. 



Sun Spots. Frequently, 

 on the surface of the sun, 

 dark spots may be seen to 

 travel across its face and 

 disappear on the other side. 

 This movement takes place PIQ. 353. Relative sizes of the planets and 

 because the sun also rotates the sun. 



on its axis. 



Sun-spots appear to be dark, but in reality they are intensely 

 bright far brighter than any terrestrial source of light. They are 

 uprushes of metallic vapors in which vanadium, titanium, and iron 

 are very evident, together with many of the common metals. They 

 are immense vortices, like the waterspouts seen at sea, with the 

 trumpet-shaped part at the top. As these immense vortices whirl, 

 the vapors of the heavier metals are carried from below outwards, 

 and are cooled sufficiently to produce oxides which fall back 



